Enable serde_json unbounded_depth feature

Author: lnicola

crates/proc_macro_api/Cargo.toml

@@ -11,7 +11,7 @@ doctest = false
 
 [dependencies]
 serde = { version = "1.0", features = ["derive"] }
-serde_json = "1.0"
+serde_json = { version = "1.0", features = ["unbounded_depth"] }
 log = "0.4.8"
 crossbeam-channel = "0.5.0"
 jod-thread = "0.1.1"